On the Persistence of QPOs During the SGR 1806-20 Giant Flare

TL;DR

This study reanalyzes SGR 1806-20 giant flare data using Bayesian methods, finding that QPOs are short-lived, decaying within a second, and identifying new QPOs that could shed light on neutron star interiors.

Contribution

It applies a novel Bayesian analysis to giant flare data, revealing rapid QPO decay and discovering new QPOs, advancing understanding of neutron star oscillations.

Findings

QPOs typically decay within a second

Multiple independently-excited modes are observed

Several new QPOs are identified

Abstract

The discovery of quasi-periodic brightness oscillations (QPOs) in the X-ray emission accompanying the giant flares of the soft gamma-ray repeaters SGR 1806-20 and SGR 1900+14 has led to intense speculation about their nature and what they might reveal about the interiors of neutron stars. Here we take a fresh look at the giant flare data for SGR 1806-20, and in particular we analyze short segments of the post-peak emission using a Bayesian procedure that has not previously been applied to these data. We find at best weak evidence that any QPO persists for more than $\sim 1$ second; instead, almost all the data are consistent with a picture in which there are numerous independently-excited modes that decay within a few tenths of a second. This has interesting implications for the rapidity of decay of the QPO modes, which could occur by the previously-suggested mechanism of coupling to the MHD continuum. The strongest QPOs favor certain rotational phases, which might suggest special regions of the crust or of the magnetosphere. We also find several previously unreported QPOs in these data, which may help in tracking down their origin.